List of top Physics Questions asked in CBSE CLASS XII

The work function for a photosensitive surface is 3.315 eV. The cut-off wavelength for photoemission of electrons from this surface is:
Electromagnetic waves with wavelength 10 nm are called:
An alpha particle approaches a gold nucleus in Geiger-Marsden experiment with kinetic energy \( K \). It momentarily stops at a distance \( d \) from the nucleus and reverses its direction. Then \( d \) is proportional to:
Energy levels A, B, and C of an atom correspond to increasing values of energy i.e., \( E_A<E_B<E_C \). Let \( \lambda_1 \), \( \lambda_2 \), and \( \lambda_3 \) be the wavelengths of radiation corresponding to the transitions C to B, B to A, and C to A, respectively. The correct relation between \( \lambda_1 \), \( \lambda_2 \), and \( \lambda_3 \) is:
An n-type semiconducting Si is obtained by doping intrinsic Si with:
A resistor and an ideal inductor are connected in series to a \( 100 \sqrt{2} \, \text{V}, 50 \, \text{Hz} \) AC source. When a voltmeter is connected across the resistor or the inductor, it shows the same reading. The reading of the voltmeter is:
Electrons drift with speed \( v_d \) in a conductor with potential difference \( V \) across its ends. If \( V \) is reduced to \( \frac{V}{2} \), their drift speed will become:
A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A. The magnetic moment of the loop will be:
Two charged particles P and Q, having the same charge but different masses \( m_p \) and \( m_Q \), start from rest and travel equal distances in a uniform electric field \( \vec{E} \) in time \( t_p \) and \( t_Q \) respectively. Neglecting the effect of gravity, the ratio \( \frac{t_p}{t_Q} \) is:
The root mean square (RMS) value of an alternating voltage applied to a full-wave rectifier is \( \frac{V_0}{\sqrt{2}} \). Then the root mean square value of the rectified output voltage is:
State Huygens' principle. Plane wave incident at angle i on reflecting surface. Construct reflected wavefront and prove i=r.
(a) Define current density. Scalar or vector? E field in a conductor (n electrons/volume, mass m, charge -e, relaxation time τ). Show j = αE, where α = ne²/mτ. (b) What's a Wheatstone bridge? Balance conditions?
A beam of light consisting of a known wavelength 520 nm and an unknown wavelength λ, used in Young’s double-slit experiment, produces two interference patterns such that the fourth bright fringe of unknown wavelength coincides with the fifth bright fringe of known wavelength. Find the value of λ.
(i) Draw a step-up transformer diagram. Describe its working principle. Explain 3 energy loss causes.
(ii) Does a step-up transformer violate energy conservation? Explain.
(iii) A step-up transformer (N_p=200, N_s=3000) has V_p=90V, I_s=2A. Calculate V_s and I_p.
A ray of light is incident normally on a refracting face of a prism of prism angle A and suffers a deviation of angle δ. Prove that the refractive index n of the material of the prism is given by:n = sin(A+δ)/sin A
The refractive index of the material of a prism is √2. If the refracting angle of the prism is 60◦, find:
(1) Angle of minimum deviation:
(2) Angle of incidence:
Define coherent sources. Can two independent sodium lamps be coherent?
(i) Derive the impedance of an R-C series circuit connected to an AC source v = v_m sin(ωt).
(ii) When does an inductor act as a conductor? Explain.
(iii) A lamp (R) and inductor (L) in series with 220V-50Hz AC give 11A. With 110V DC, it gives 11A. Find L.
(a) "EM wavelength correlates with the size of the radiating system." Give two examples.
(i) Why do long-distance radio broadcasts use shortwave bands?
(ii) Why are X-ray telescopes satellite-based, while optical/radio telescopes are ground-based?
A transformer has 500 primary turns and 5000 secondary turns. Input is 220V-50Hz. What's the output?
An air-filled parallel plate capacitor (d = 1mm, C = 20pF) is charged to 4.0µC. Find work done to increase plate separation to 5mm (constant charge).
Differentiate between diffusion and drift current. Explain their role in p-n junction formation.
Coils P and Q. Current in P induces current in Q. (a) Explain the phenomenon. (b) Two factors affecting current in Q. (c) Direction of current in Q when current is in P and (i) R increases, (ii) R decreases.
(a) State Bohr's postulates for the hydrogen atom.
(b) A hydrogen atom de-excites from level n to (n-1). Show that emitted frequency ν ∝ α/n³ for large n (α = constant).
(a) Two characteristic properties of nuclear force. (b) Plot potential energy of a nucleon pair vs. separation. Two conclusions from the plot.